What the game is
Preserve the Evidence is a hazard-count mystery — the number logic the whole world knows from minesweeper, rebuilt as a fair detective case. Someone slipped into the record room overnight and rigged evidence boxes across a whole shelf wall with dye-cannisters: lift a lid and the papers inside are ruined. The night clerk's stocktake survives, and it is your only map: every box the clerk checked carries a number counting exactly how many of its neighbours — sides and corners — are rigged. Every square on the shelf is a number or a closed box; there are no blanks.
Unlike the arcade game, nothing here is hidden behind clicks and nothing explodes. The whole stocktake is printed before you start, the requisition tally tells you exactly how many boxes are rigged, and your only moves are marks: flag a box rigged, dot it safe, or clear the mark. Then the second act: the saboteur tore the docket tag off every box they rigged, and the bureau recovered one loose heap of tags — no bundles, no order. The heap unseals the moment your flags are exactly right, and sorting its letters into their words is the puzzle that closes the case.
Case procedure
- Start at the met numbers. A number with all its rigged neighbours already flagged is finished — every other box beside it is safe. Zeros are met before you touch anything.
- Fill the numbers with no slack. When a number still needs exactly as many rigged boxes as it has unmarked neighbours, every one of them is rigged.
- Reread numbers as flags land. Every flag you place changes what the numbers around it still need. The shelf resolves in waves, not in one pass.
- Subtract overlapping numbers. The expert move: when every box that could satisfy one number also counts for a second, subtract the two — the boxes only the larger number can see are forced one way or the other. This is the deduction that cracks the tangled middle of a shelf.
- Spend the requisition tally late. The shelf's total works like a number that watches every box at once. When all rigged boxes are flagged, everything else is safe; when the remaining unknowns exactly match the missing count, they are all rigged.
- Sort the recovered heap. When every rigged box is flagged, the heap unseals as one pile of mixed letters. Somewhere in it: a six-letter creature, a four-letter codename, a six-letter motive word — and the heap splits only one way. Lay the tags on the wire line and file the wire.
- Work the informer's notes. Filing the alias unseals two or three precise notes about the person behind it — several read through the alias word itself. Test each member of staff against every note, cross out the cleared, and accuse the one name left standing.
The rulings that matter most
- Neighbours touch on sides and corners. A box in open shelf has eight neighbours; edges and corners have fewer. Every stocktake number counts all of them.
- A checked box is never rigged. The clerk opened it and found it untouched. Numbers sit only on checked boxes; every other square is a closed box that could hold anything.
- The stocktake never lies, and neither does the tally. Marks of yours that contradict a printed number turn red the moment they appear — a mechanical reading of your own marks against the public rules, never a peek at the answer.
- Safe dots are never required. The heap unseals when every rigged box is flagged and nothing else is. Dots are your working notes and can be wrong without penalty — Check will say so.
- The heap unseals only for the truth. The tag desk opens the moment your flags exactly match the shelf — nothing leaks early, and even then the tags arrive as one mixed pile.
- The heap splits exactly one way. Across the bureau's watch-lists there is a single arrangement of the recovered letters into its words — proved before the case ships. The manual tells you the shapes: a six-letter creature, a four-letter codename, a six-letter motive word.
- Filing is the lock, not a hint. Filing checks each word on the line: right words lock their tags, wrong ones bounce back to the heap stamped "wire returned". Locking the alias is what unseals the informer's notes.
- The notes convict together, never alone. Every case ships with two or three informer's notes, each carrying its own fine-print ruling. Exactly one member of staff fits them all, and dropping any note would leave at least two standing — the same uniqueness-and-necessity standard as every other game in the bureau.
Choosing a rank
Filing Clerk (6×6 shelf, six rigged boxes, four staff) teaches the stocktake law in about ten minutes, and its six tags spell one word: the alias. Archive Officer (8×8, ten rigged boxes) is the full method: a more shut board, real subtraction moves, and a heap of ten mixed tags hiding two words to separate. Chief Registrar (10×10, sixteen rigged boxes) is the long shift — a board that reads mostly closed, where overlapping numbers carry whole regions, and sixteen mixed tags hiding three words: alias, file and motive. Bigger shelves add deeper deduction, never unfair steps.
Fairness, hints and reveal
Every case is generated and then proved before you see it. The generator's solver must complete the whole shelf using only the deductions described in this manual — the same reasoning you use at the desk — which guarantees exactly one arrangement fits the stocktake and that no guessing is ever required; a layout that falls short is thrown away and rebuilt. The tag desk passes the same standard: across the bureau's full watch-lists the recovered heap splits into its words in exactly one way — proved per case — and no shipped jumble accidentally arrives with a word already spelled. The informer's notes pass it too: the notes identify exactly one member of staff, and removing any single note would leave at least two, so no note is dead weight and none convicts alone. Check flags marks that cannot be right without adding any of its own. Hints escalate politely: the first press names a deduction and the reasoning behind it; a second press points at the exact box, and the mark is still yours to place. Reveal unseals the saboteur's own chart and excludes the case from your cases-cracked tally. Wrong accusations and returned wires are stamped on the file; the case stays open.
Printing a case
Any case can be downloaded as a PDF pack built entirely in your browser from the same case number as the on-screen shelf: the briefing, the jumbled tag heap and the staff roster on the case sheet, one full shelf with stocktake numbers sized for pencil work, and an optional answer key showing the chart, the sorted words and the warrant. Paper cannot unseal itself, so the printed heap is shown jumbled from the start — nothing beyond its letters. A number grid plus an anagram is about as print-friendly as puzzles get — a pack runs about three A4 sheets and suits classrooms, puzzle clubs and long train journeys, and the case number on the cover reopens the same shelf on screen.
Questions from the record room
What is Preserve the Evidence?
Preserve the Evidence is a hazard-count mystery — minesweeper’s famous number logic, rebuilt as a detective case with no guessing and no exploding first click. A saboteur has rigged evidence boxes across a record-room shelf with dye-cannisters. The night clerk’s stocktake survives: every checked box carries a number counting exactly how many of its neighbours are rigged, every other square is a closed box, and pure deduction flags every rigged one. Then the second act: the saboteur tore the docket tag off every box they rigged, and the recovered tags — jumbled, order unknown — unseal once your flags are right. Unjumble them and they spell the alias that names the saboteur.
How is this different from classic minesweeper?
Classic minesweeper reveals numbers as you click, punishes a wrong click instantly, and famously forces 50/50 guesses. Preserve the Evidence uses the fixed-board form instead: the whole stocktake is printed before you start, boxes never open or explode, and your only moves are marks — flag a box rigged or dot it safe. Every case is proved solvable by logic alone before you see it, so the deduction is the whole game, exactly as the numbers-on-a-grid puzzle deserves.
How do the stocktake numbers work?
A number sits on a box the night clerk checked and found untouched. It counts exactly how many of that box’s neighbours — sides and corners, up to eight — are rigged, and a checked box is never rigged itself. The requisition tally beside the shelf gives the total number of rigged boxes. If a number reads 2 and two of your flags already sit beside it, every other box touching it is safe; if it still needs two and only two boxes remain beside it, both are rigged. The subtler moves come from reading two overlapping numbers together.
What are the torn docket tags?
Every evidence box wears a lettered docket tag, and the saboteur tore one off every box they rigged before pocketing the lot. The bureau recovered a single loose heap from a coat left at the scene — no bundles, no order. The heap stays sealed on the tag desk until every rigged box is flagged and nothing else is; then it flips face-up as one pile of mixed letters, and sorting it is the puzzle: somewhere in the heap is a six-letter creature (the alias), and at higher ranks a four-letter file codename and a six-letter motive word besides — you work out which letters belong to which word. Filing the alias unseals the informer’s notes — two or three precise observations about the person behind the codename, several of them reading through the very word you just solved (“the Badger’s surname shares exactly two letters with the word BADGER”). Exactly one member of staff fits every note, so the arrest is a deduction of its own, not a lookup. Nothing about the answer leaks early: the tags are hidden until your flags are exactly right, they arrive as one scrambled pile, and the staff list never names an alias.
Is every shelf guaranteed solvable without guessing?
Yes. Every case is proved before you see it: the generator’s solver must complete the whole shelf using only named, human deductions — met numbers, numbers with no slack, the requisition tally, and subtracting one number’s reach from another’s. A layout that would ever require a guess is thrown away and rebuilt. The tag desk is proved the same way: across the bureau’s full watch-lists, the recovered heap splits into its words in exactly one way, so the sorting puzzle always has a single honest answer.
What do Check, Hint and Reveal do?
Check flags any current mark that cannot be right, without adding marks of its own — it is always safe. Hints come in two strengths: the first press names a deduction and explains the reasoning — which number to work, or which two numbers to read together; pressing again points at the exact box, though the mark is still yours to place. Reveal unseals the saboteur’s own chart, and a revealed case never joins your cases-cracked tally.
What are the case ranks?
Filing Clerk hides six rigged boxes in a 6×6 shelf with a generous stocktake — a complete case, unjumble and all, in about ten minutes, with six tags spelling one word: the alias. Archive Officer works an 8×8 shelf with ten rigged boxes and a more shut board, and its heap of ten tags hides two words to separate — the alias and the four-letter file codename. Chief Registrar is the full assignment: a 10×10 shelf, sixteen rigged boxes, a board that reads mostly closed so the subtler subtraction moves carry the day, and sixteen mixed tags hiding three words — alias, file and motive.
Can I play on a phone?
Yes. The shelf sizes itself to the screen and every box is a proper button — tap once to flag a box rigged, twice to dot it safe, three times to clear the mark, or press and drag along a row or column to mark a whole run in one stroke. A stroke only overwrites boxes in the same state as the one it started on, so marking safes never destroys your flags, and Undo takes back the whole stroke. Your marks save automatically between visits, and each case has a case number so the same shelf can be reopened.
Can I print a case?
Yes. Any case can be downloaded as a PDF pack built entirely in your browser from the same case number as the on-screen shelf: the briefing, the jumbled tag heap and the staff roster on the case sheet, one full shelf with stocktake numbers sized for pencil work, and an optional answer key showing the chart, the sorted words and the warrant. Paper cannot unseal itself, so the printed heap is shown jumbled from the start — it gives nothing away beyond its letters. Nothing is uploaded anywhere, and the dialog shows the sheet count before you download.
Is Preserve the Evidence free?
Yes. All ranks are free to play in your browser with no account or sign-up. A new case is one click away, and every case is generated fresh — the shelf is rigged, proved fair, and dressed with new tags, aliases and staff, so no two shelves read the same.